Almost a third of government vehicles will be kept off Shanghai's roads when the air is heavily polluted, and schools and kindergartens will close, the city's environmental protection bureau said yesterday.

The bureau outlined emergency measures to be taken when pollution is heavy or severe, the top two levels in a six-tier scale.

In the first three months of the year, only 59 days were not polluted, the bureau said, while the air quality in January was the worst since monitoring began.

Ten of the days were deemed heavily polluted with the air quality index exceeding 201.

The bureau said the rising number of polluted days was mainly due to the haze that covered most of the country in January and the fact that a new and stricter air quality evaluation system was in operation, which included PM2.5 for the first time.

PM2.5 is the major focus of the emergency plan, while the authority will also include the control of ozone, the major pollutant on hot days.

The average density of PM2.5 in the first three months was 73 micrograms per cubic meter. The nation's daily limit is 75 and the yearly limit 35.

The emergency plan includes alerting the public, restricting production in highly polluting industries and reducing the number of vehicles on the roads when there is heavy pollution that is expected to persist for some time.

The plan will be put into operation when the air quality index is between 201 and 300, indicating heavy pollution, for 18 hours and likely to continue.

The public will be alerted through government microblogs, websites and local media. Schools will be told to stop outdoor activities.

Power plants will be required to use high-quality coal that causes less pollution and industries such as petrochemicals will be ordered to cease production.

Vehicles transporting construction materials and waste will be ordered off the roads, while construction which causes dust to fly must stop.

When the index surpasses 300, indicating severe pollution, stricter measures will be adopted including a ban on all highly-polluting vehicles, a ban of fireworks and a 30 percent reduction in the use of government vehicles.

If the pollution is extremely serious, the city government can order local schools and kindergartens to shut.